At a Glance

Why Get Tested?

When to Get Tested?

When a person has symptoms suggesting a vitamin A deficiency or excess, or is at risk for a deficiency

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

Fasting is required, and no alcohol should be consumed for 24 hours before sample collection.

The Test Sample

What is being tested?

This test measures the level of retinol in the blood; retinol is the primary form of vitamin A in animals. Vitamin A is an essential nutrient required for healthy vision, skin growth and integrity, bone formation, immune function, and embryonic development. It is required to produce photoreceptors in the eyes and to maintain the lining of the surface of the eyes and other mucous membranes. Deficiencies in vitamin A can impair night vision, cause eye damage, and in severe cases lead to blindness. Acute or chronic excesses of vitamin A can be toxic, cause a range of symptoms, and sometimes lead to birth defects.

The body cannot make vitamin A and must rely on dietary sources of vitamin A. Meat sources provide vitamin A (as retinol), while vegetable and fruit sources provide carotene (a substance that can be converted into vitamin A by the liver). Vitamin A is stored in the liver and fat tissues (it is fat-soluble), and healthy adults may have as much as a year's worth stored. The body maintains a relatively stable concentration in the blood through a feedback system that releases vitamin A from storage as needed and increases or decreases the efficiency of dietary vitamin A absorption.

Deficiencies in vitamin A are rare in the United States, but they are a major health problem in many developing nations where high numbers of people have limited diets. One of the first signs of vitamin A deficiency is night blindness. In a 1995-2005 review of the global prevalence of vitamin A deficiency in populations at risk, the World Health Organization estimated that night blindness affected as many as 5 million preschool age children and nearly 10 million pregnant women. In addition to this, they estimated that another 190 million preschool age children and 19 million pregnant women were at risk of vitamin A deficiency, with low retinol levels that reflected an inadequate supply of vitamin A.

Is any test preparation needed to ensure the quality of the sample?

The Test

How is it used?

Vitamin A testing is used to help diagnose vitamin A deficiency in people with symptoms, such as night blindness, or in people with diseases that impair intestinal absorption of nutrients. It may also be used to detect toxic levels caused by ingestion of large amounts of vitamin A.

Testing may be done when a person has a disease that is associated with malabsorption of nutrients to monitor vitamin A status. Testing may be done periodically to insure that the person is getting sufficient vitamin A. Some diseases that are associated with inadequate vitamin A absorption include:

Testing may be performed when a person has symptoms that suggest vitamin A toxicity and their medical history is consistent with consumption of foods or vitamin supplements containing vitamin A. Some of the symptoms associated with vitamin A toxicity are:

What does the test result mean?

A normal vitamin A level indicates that a person currently has sufficient vitamin A but does not indicate how much is stored in reserve. The body will maintain vitamin A in the blood at a relatively stable level until stores are depleted. A low vitamin A test result indicates that all reserves have been depleted and the person is deficient.

A high vitamin A level typically indicates that the capacity to store vitamin A has been exceeded and excess vitamin A is now circulating in the blood and may be deposited in other tissue, leading to toxicity.

Is there anything else I should know?

A person with a minimal amount of vitamin A stored may have marginal but adequate vitamin A until they have an illness or other condition, such as pregnancy, that puts increased demands on their body. This is one of the reasons that night blindness during pregnancy is prevalent in many parts of the world.

Eating excessive amounts of foods with beta carotene, such as carrots, can cause a person's skin to turn yellow-orange but it does not cause vitamin A toxicity. The body does not convert beta carotene to vitamin A when there is sufficient vitamin A present.

2. What are the recommended dietary allowances (RDA) for vitamin A?

For teens and adults age 14 and older, the RDA is 900 micrograms (mcg) (3,000 IU) for males and 700 mcg (2,310 IU) for females. The recommendations for others, such as infants, children and pregnant women, vary. For these, see the lists provided by the National Institutes of Health Office of Dietary Supplements.

Article Sources

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Barclay, L. (2010 December 8). Vitamin A May Reduce Deaths From Measles and Diarrhea in Children. Medscape Today from Medscape Medical News [On-line information]. Available online at http://www.medscape.com/viewarticle/733832 through http://www.medscape.com. Accessed March 2011.

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This article was last reviewed on May 12, 2011. | This article was last modified on May 27, 2014.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.